Activation of monooxygenases in human liver by 7,8-benzoflavone

Addition of 10-4 M 7,8-benzojlavone to homogenates of human liver samples obtained by autopsy or surgical biopsy increased the rate of benzo [a] pyrene hydroxylation up to II-fold. 7,8-Benzojlavone also increased the rates of hydroxylation of zoxazolamine and antipyrine at 10-4 M but inhibited these reactions at 10-6 M. The effects of 7,8-benzojlavone on the hydroxylation of benzo[a]pyrene and zoxazolamine in microsomes from human liver were similar to those in homogenates. Addition of 7,8-benzojlavone to homogenates of surgical biopsy samples of human liver had little or no effect on the rates of oxidative metabolism of 7-ethoxycoumarin, coumarin, and hexobarbital. Marked individuality for the activating and inhibiting effects of 7,8-benzojlavone was observed in different liver samples. This individuality may result both from the presence of multiple monooxygenases in varying amounts and proportions in the different liver samples and from a selective effect of 7,8-benzojlavone on certain of the monooxygenases.